Greenhouse evaluation of processed swine lagoon solids as a fertilizer source

Abstract

The highly concentrated nature of the swine (Sus scrofa domesticus) production industry in the Coastal Plain region of North Carolina, along with economic constraints that discourage transport of the swine effluent more than a few kilometers from the site of production, result in frequent and repeated application of swine effluent to the same agricultural fields or pastures. Creation of value‐added products and marketing as a fertilizer is an alternative means of redistributing nutrients that are concentrated regionally. Fertilizer equivalency greenhouse studies were conducted to evaluate the potential for processed swine lagoon solids (PSLS) formulated from dewatered swine lagoon solids and rock flour to serve as a fertilizer source for agricultural crops. Sweet corn (Zea mays L.), sorghum (Sorghum bicolor L.), and field bean (Phaseolus vulgaris L.) were grown for six weeks, and common bermudagrass (Cynodon dactylon L. Pers.) was grown for 18 weeks on a Norfolk sandy loam (fine‐loamy, Kaolinitic Thermic Kandiudult) using PSLS and NH₄NO₃ at 0 to 1,000 mg N kg⁻¹, and PSLS and KH₂PO₄ at 0 to 200 mg P kg⁻¹. Application of increasing rates of NH₄NO₃, KH₂PO₄, and PSLS significantly increased dry matter yields of all the crops tested (P≤0.05). The increases due to PSLS application were similar or even superior at the highest rates to yields from conventional fertilizer, but nitrogen (N) and phosphorus (P) uptake were significantly less from the PSLS source. Total N uptake, averaged across all application rates, ranged from 90 to 290 mg pot⁻¹ for PSLS and 420 to 432 mg pot⁻¹ for NH₄NO₃ applied to the four test crops. Total P uptake ranged from 9 to 13 mg pot⁻¹ for PSLS and 16 to 23 mg pof⁻¹ for KH₂PO₄. Incorporation of the PSLS into the soil increased the amount of extractable copper (Cu) and zinc (Zn). We conclude that PSLS is potentially a valuable fertilizer source, especially as a source of P for agricultural crops. The material is also an acceptable source of N if added in sufficient quantity, depending on the crop selected.